Prior to a June, 1984, FCC decision, pay telephones were the exclusive province of local telephone companies. Others were precluded from the business of providing pay telephone services. Today, however, subject to state Public Utility Commission regulations, Customer Owned Coin Operated Telephone ("COCOT") service is permitted. An outgrowth of COCOT service has been the private operation of institutional telephone services. As might be expected, this "privatization" of phone systems has created a number of technical challenges including the automated detection of a called party's response to some appropriate prompt (such as, a request for acceptance of a collect call) by dialing a pulse-dial telephone and, in the case of prison systems, the prevention of three-way calling.
Coin telephones owned by local telephone companies generally utilize DC signals to signal called-party-answer. This information is transmitted between telephone company central offices and then to the originating pay telephone telling it, in effect, to accept payment for the call. This information is not, however, normally communicated to conventional, i.e., regular business and residential, telephones nor has this information been available to COCOT equipment.
Collect calls placed through COCOT equipment are typically handled by an automated operator service ("AOS"), thus providing the owner of the COCOT equipment with the ability to provide collect call service and bill users of that service for both intra- and inter-LATA calls. However, the use of an AOS for collect calls is expensive. In addition, it opens the possibility of fraudulent activity in certain instances.
In many institutions the phone calls placed by a patient/client or prison inmate are primarily, if not exclusively, collect calls. Collect calls initiated by a patient/client must be indicated as such to the called party. In addition, calls placed by an inmate to an outside party often begin with a prerecorded message stating that the call or collect call is from "a prison" and is being placed by "prisoner's name." In the above cases the called party is usually asked to dial a digit, commonly a "0" or a "1", to accept the call or the attendant charges. The phone system providing such service must be able to detect such acceptance both as a dual-tone-multi-frequency ("DTMF") tone response from a "Touch-Tone" phone as well as to detect the equivalent response on a pulse-dial telephone. ("Touch-Tone" is a trademark of the AT&T corporation.)
The clients/inmates in some institutions may be allowed to call only numbers on a pre-authorized list in order to deter fraudulent activity. A prison phone system, for example, must be able to detect the called party's flashing the hook switch in order to prevent the called party from activating three-way (i.e., conference) calling, dialing another number and then connecting the prisoner to an unauthorized phone number.
Accordingly, a need has arisen for a telecommunications system which can automate and simplify the processes currently handled by a traditional AOS. Specifically, a need has risen for telephone call handling equipment which can automatically route local and long distant calls without the intervention of an outside service or live operator, and which enables the telephone owner/service provider to charge for the completion of a call or collect call while preventing three-way calling.
Several methods of detecting a three-way call initiated by a hook-flash are known in the prior art. The hook-flash results in a temporary disconnect and reconnect which can be observed as a momentary interruption of loop current at the telephone company central office. The loop current loss, however, is not observed elsewhere in the network nor is the loop current loss made known to the respective parties. Thus, this attribute of a hook-flash cannot be employed, except at the central office. Alternatively, the attempt to initiate a three-way call has been detected utilizing the technology shown in the '702 Patent. That system, as based on analog technology, accurately detects the vast majority of attempted three-way calls. The current invention, which is based on the detection of additional characteristics of the hook-flash signal and utilizes digital signal processing ("DSP"), is more discerning of the attempted three-way call and more reliable in distinguishing an attempted three-way call from other events that occur on the telephone line (such as, voice fluctuations, noises from physical contact, e.g. dropping or tapping, of the handset, etc.).